What makes people float?

People float because their bodies, especially with lungs filled with air, are less dense than the surrounding water. If an object weighs less than its equivalent volume of water, it floats, and if it is heavier, it sinks.

An individual's buoyancy depends greatly on her body type. Bone and muscle are more dense than water, while fat is less dense. Individuals with higher body fat ratios find floating easier, while those with less fat and more muscle float lower in the water. Lung capacity also plays a role, since the density of the air stored in the organs is much less than the surrounding water.